The present invention relates to an apparatus for rapid, disposable, low volume solid phase extraction and to a method for using such an apparatus.
Solid Phase Extraction (SPE) has become popular in sample preparation. The main advantage of SPE is that less solvent is required as compared to traditional liquid extraction. In SPE, a cartridge composed of plastic is used to store the adsorptive particle of stationary phase as well as to provide a sample reservoir. The cartridge is placed on a vacuum manifold, and the vacuum is used to pull sample and solvent through the stationary phase. The stationary phase is first washed and activated by addition of various solvents (approximately 1-3 mL each) in a conditioning step. The conditioning step is also essential to prevent channeling, a process in which the sample components pass though the stationary phase packing without actually interacting with the adsorptive particles of the stationary phase in a chemically-meaningful manner.
The sample matrix is subsequently added to the cartridge, and the matrix is passed slowly though the stationary phase to allow the analyte to interact with the stationary phase. Several types of analyte-stationary phase interactions are possible, such as adsorption and partitioning. After the sample matrix has passed through the cartridge to waste, a wash step is performed to remove compounds of the sample matrix. The final step is elution of the analytes. A clean test tube is first placed under the SPE cartridge, then elution solvent (1-2 mL) is added to remove the analytes from the stationary phase.
After the extraction procedure, a concentration step is performed to improve the sensitivity of analysis. The solvent from the extract (1-2 mL) is evaporated using nitrogen gas flow and heat. A small volume of solvent (0.10-0.20 mL) is then added to the test tube, and the test tube is vortexed to dissolve the extracted analytes. The solution is subsequently transferred to a clean vial for analysis by gas chromatography (GC) or high performance liquid chromatography (HPLC).
Although SPE has helped to make sample preparation faster and easier, the concentration step by itself takes several minutes to perform, with the entire extraction time taking over 20 minutes. Another drawback to SPE is that significant solvent volumes are still required (at least 5 mL total). An extraction procedure that significantly reduces the extraction time and reduces solvent volume will have a significant impact in analytical preparation methods.
There have been numerous attempts to remedy the foregoing deficiencies in SPE. A notable modification of this technology is disclosed in U.S. Pat. No. 6,048,457 issued to Kopaciewicz et al. This patent discloses a method of SPE that uses a polymer-matrix bound sorbent material. In one embodiment, a porous polymer matrix entraps particles of adsorbent material and is cast-in-place inside a pipette tip. In a contrasting example, sorbent particles are immobilized between two porous frits. This invention provides an effective platform for micromass handling. Unfortunately, the matrix-bound particles are unable to achieve maximum contact with the sample solution due to minimal exposed surface area and severely restricted mobility of the particles. As a result, the efficiency of the solid-liquid equilibrium leaves much room for improvement.
Therefore, there still exists a substantial need for a chemical extraction device that adequately overcomes the problems existing in preparing chemical samples for chromatographic separation techniques.
According to its major aspects and broadly stated, the present invention is a device for rapid, disposable, low-volume solid phase extraction of analytes from various fluids to be tested. The term fluid refers to liquids and to semi-liquids. In particular, the present invention relates to a pipette tip which contains adsorptive particles of a solid stationary phase that are loosely confined inside the tip. An attached pipettetor draws the sample into the pipette tip. The present invention is also a method for using the foregoing pipette tip to extract an analyte. Maximum contact and thorough mixing between the stationary phase and the analyte solution is accomplished by agitating them (shaking, inverting repeatedly, vortexing or by drawing air into the pipette). Agitation insures rapid equilibration and, thus, efficient and rapid adsorption of the analyte.
Other features and advantages of the present invention will be apparent to those skilled in the art from a careful reading of the Detailed Description of a Preferred Embodiment accompanied by the following drawings.